The play caused by manufacturing tolerances between a worm-gear spindle and the internal thread of a nut, which manifests itself as so-called lost motion, is unacceptable for certain applications, e.g., in measuring systems, fine-adjustment apparatus and scanner units. In such high precision systems, it is essential that the transmission of motion between spindle and nut should be free from play.
German Patent 36 42 463 discloses a device for axially adjusting free from play mounting arrangements using a pair of adjustment rings. By means of two or more complementary concentric pitch surfaces these adjustment rings rest on each other with a pitch angle in the automatic locking range and change their axial extension by rotation relative to each other. Each pair of adjustment rings features two or more pairs of pitch surfaces radially nested into each other and extending over an angle of 360 degrees, said surfaces being angularly offset with respect to the beginning and end of their pitch. The size of the offset angle is inversely proportional to the number of pairs of pitch surfaces.
These known adjustment rings are of a complex design and thus difficult to manufacture if the precision required of a worm gear of the aforementioned type is to be ensured. They are not suitable for the manufacture of large production series involving broad tolerances, which increases their manufacturing costs significantly.